I don’t know who did this and why it wasn’t tested but it’s no fun when you want to click on a system on the right part of the map but instead of it you get the overlapping annoying filter.
It shouldn’t work like that. Just make the filter appear only when the cursor is moved very close to the right edge, about the width of the new vertical bar. Or better yet, make it activate on click. Or just find better UI/UX designers who will do their job.
No, even when the window is not small (which is relative anyway) this filter eats a lot of space. And you can accidentally trigger it when you don’t expect. I’m sure many people came across this several times but they just got used to new bugs introduced here and there.